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Ehud Keinan
Department of Chemistry and Institute of Catalysis Science and Technology, Technion - Israel Institute of Technology, Technion City, Haifa 32000, Israel, and e-mail: keinan@tx.technion.ac.il URL: http://www.technion.ac.il/technion/chemistry/staff/keinan/ |
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The first nanoscale, programmable 2-state-2-symbol finite automaton that computed autonomously with all of its components, including hardware, software, input and output being biomolecules, mixed together in solution was previously presented [1]. The hardware consisted of a restriction nuclease and a ligase, while the software (transition rules) and the input were double-stranded DNA oligomers. Computation was carried out by processing the input molecule via repetitive cycles of restriction, hybridization, and ligation reactions to produce a final-state output in the form of dsDNA molecules, which were characterized by gel electrophoresis. We increased the levels of complexity and mathematical power of these automata by the design of a 3-state-3-symbol automaton that has as many as 27 possible transition rules and a remarkable number of 939,524,089 syntactically distinct programs. This number is significantly larger than the corresponding number of 765 available programs with the 2-symbol-2-state device. Restrictions at the beginning of the symbol domain, 1 basepair deeper, and 2 basepairs deeper into the domain represent the three internal states, S0, S1 and S2, respectively, as shown below. The applicability of this design was further amplified by employing surface-anchored input molecules, using the surface plasmon resonance (SPR) technology to monitor the computation steps in real time. Computation was performed by alternating the feed solutions between BbvI endonuclease and a solution containing T4 DNA ligase, ATP and appropriate transition molecules. The output detection involved final ligation with one of three soluble detection molecules. Parallel computation and real-time detection were carried out automatically with a Biacore chip that carried 4 different inputs.
